On Wed, 28 Apr 2010 03:44:34 +0200 Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote: > On Wed, Apr 28, 2010 at 10:29:28AM +0900, KAMEZAWA Hiroyuki wrote: > > Hmm..Mel's patch 2/3 takes vma->anon_vma->lock in vma_adjust(), > > so this patch clears vma->anon_vma... > > yep, it should be safe with patch 2 applied too. And I'm unsure why Mel's > patch locks the anon_vma also when vm_start != start. See the other > email I sent about patch 2. > > > I think we can unlock this just after move_page_tables(). > > Checking this, I can't see where exactly is vma->vm_pgoff adjusted > during the atomic section I protected with the anon_vma->lock? > For a moment it looks like these pages become unmovable. > The page can be replaced with migration_pte before the 1st vma_adjust. The key is (vma, page) <-> address <-> pte <-> page relationship. vma_adjust() (*) move_pagetables(); (**) vma_adjust(); At (*), vma_address(vma, page) retruns a _new_ address. But pte is not updated. This is ciritcal for rmap_walk. We're safe at (**). > I guess this is why I thought initially that it was move_page_tables > to adjust the page->index. If it doesn't then the vma->vm_pgoff has to > be moved down of shift >>PAGE_SHIFT and it doesn't seem to be > happening which is an unrelated bug. > Anyway, I have no strong opinion about the placement of unlock(anon_vma->lock). I wonder why we don't see this at testing memory-hotplug is because memory-hotplug disables a new page allocation in the migration range. So, this exec() is hard to get a page which can be migration target. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>